Japan is keeping a close watch on Chinese President Xi Jinping's attempts to bolster relations with North Korea as Tokyo continues to grapple with the best way to go about arranging a summit with Pyongyang, diplomatic sources said.

Closer ties between Beijing and Pyongyang could crush the hopes of Prime Minister Shinzo Abe, who has been trying to pave the way for a meeting with North Korean leader Kim Jong Un in cooperation with the United States.

As Beijing has been eager to use Pyongyang as a bargaining chip to move ahead with trade negotiations with Washington, it is unlikely China would help Japan — a close U.S. ally — realize a summit with North Korea, the sources said.